1. Field of the Invention
The present invention relates to a tire pressure indicator and more particularly to a remote tire pressure indicator which is neither mechanically or electrically coupled to the tire.
2. Description of the Prior Art
U.S. Pat. No. 4,334,428, entitled Apparatus for Indicating Parameters Sensed on a Rotatable Wheel, issued to Raoul G. Fima and Jacques E. Mahieux on June 15, 1982, teaches a circuit which is mounted on a rotatable wheel of a vehicle and which varies its resonant frequency in accordance with tire pressure. U.S. Pat. No. 4,283,707, entitled Aircraft Low Pressure Tire Warning System Having Comparator Circuit for Each Axle Pair of a Four Wheel Bogie Configuration, issued to Royce F. Church on Aug. 11, 1981, teaches pressures transducers which coupling transformers electrically couple to a signal processor.
U.S. Pat. No. 4,226,126, entitled Mechanical Displacement-Electrical Signal Transducer, issued to Werner Herdon on Oct. 7, 1980, teaches in order to measure small displacement, for example displacement of a membrane under change of pneumatic pressure applied at opposite sides thereto, a ferromagnetic wire which is stretched between a fixed support and the membrane. An exciter coil, connected to a source of alternating current of suitable strength cyclically reversely magnetizes the ferromagnetic wire. A pick-up coil is electromagnetically coupled to the wire to sense the change of magnetization thereof which will be in the form of sharp needle pulses as the magnetization of the wire changes, the pulse amplitude and pulse width being highly dependent on the strain in the wire and hence on the deflection of the membrane. The wire may be stressed under tension.
U.S. Pat. No. 4,250,759, entitled Digital Readout Gauge, issued to Otto Z. Vago and Frank S. Irlinger on Feb. 17, 1981, teaches a digital readout gauge which may be a tire pressure gauge which is mounted in a small portable housing. A pressure chamber is formed within the housing with a valve core deflator mounted within the housing to depress the core of a standard tire valve and permit the air pressure within the tire to be introduced into the chamber. A wall of the chamber is movable with changes of pressure and a piezoelectric crystal transducer or strain gauge transducer is mounted to be stressed in accordance with movement of this wall to develop an analog voltage in accordance with the air pressure. An electrical circuit is contained within the housing and energizable by a battery carried within the housing. A power switch is actuated to an on condition by movement of the gauge onto the tire valve to energize the electrical circuit with the analog voltage passed to an analog-to-digital converter and then to a digital readout display to display the digital value of the air pressure within the tire.
U.S. Pat. No. 4,195,531, entitled Pressure Detector Using an Average Circuit, issued to Kenji Okamura on Apr. 1, 1980, teaches a pressure detector which includes a spring-loaded diaphragm mounted in a housing to define a pressure chamber to which test fluid is introduced. A pulse generating element is provided to generate an electrical pulse in response to a displacement of the diaphragm when the fluid pressure in the pressure chamber exceeds a predetermined level. An averaging circuit is connected to the pulse generating element to convert the pulses into a signal having a voltage level representative of the mean value of the pressure variation.
At the present time, there are no devices which are able to record the pressure of pneumatic tires on the instrument console of a vehicle. For a period of time a system to measure tire pressure with a gauge inside the vehicle was available to large vehicles, such as buses and trucks. This system used a flexible tube connected to the center of the wheel by a sealed bearing and it gave a relatively good indication of the tire pressure. This mechanism, complicated and with many limitations, is now obsolete. So the modern car of today, having many instruments on the panel, does not have one able to indicate the tire pressure.
Recently, there has been proposed a type of mechanism utilizing a transmitter located inside of the tire and a receiver close to the transmitter located on the body of the car. This type of mechanism has many limitations, including the need to check the electrical supply and the uncertainty that everything is working properly.